Light producing system

ABSTRACT

A method is provided whereby a high density of metallic atoms may be obtained in the plasma of a flash lamp by deposition of the desired metal substantially uniformly over the inside of an evacuated tube. Applying a pulse of current which vaporizes the metal produces the desired results.

United States Patent 1191 1111 3,781,585 Gallo [4 Dec. 25, 1973 [54] LIGHT PRODUCING SYSTEM 3,431,447 3/1969 Larson .1 313/184 x 3,575,630 4/1971 Edris 1 313/229 [751 Invent: Charles Pmfield/ 2,042,147 5/1936 Fairbrother 313/197 2,732,513 1/1956 Anderson et al. 313/184 X [73] l xerox Cwpomfion Rochester 3,209,188 9/1965 Freeman 313 110 x [22] Filed: Dec. 22, 1971 2,291,406 7/1942 Paehr 313/110 X [2 Appl No 210 931 2,291,983 8/1942 Pipkin 431/95 Related Applicafion Data Primary Examiner-A1fred L. Brody [62] Division of Ser. No. 837,881, June 30, 1969. Attorney-Paul M. Enlow et al.

[52] US. Cl 313/184, 313/325, 316/5, 1 I

, 431/95 [57] ABSTRACT 1 I CI. E2 a of Search 431/95 4? A method is provided whereby a high density of me- 316 /6 4 3 184, tallic atoms may be obtained in the plasma of a flash lamp by deposition-of the desired metal substantially uniformly over the inside of an evacuated tube. Apply- [56] References Cited ing a pulse of current which vaporizes the metal produces the desired results. I UNITED STATES PATENTS 3,l53,169 l0/l964 Bauer 1. 313/161 5 Claims, 6 Drawing Figures LIGHT PRODUCING SYSTEM This is a division of application Ser. No. 837,88l, filed 6/30/69.

BACKGROUND OF THE INVENTION This invention relates to light producing systems and more specifically to a process for obtaining selected spectra.

One of the more common methods utilized to produce a flash lamp involves introducing a selected gas, preferably xenon, into a tube envelope. An energized capacitor is discharged into the tube envelope resulting in a burst of enrgy imparted to the gas, thereby ionizing continuous spectra are produced. It is often a requirement in xerography, among other branches of technology, to provide and utilize a specific light source so as to maximize utilization of the energy and thereby reduce the requirement. Such a situation also exists. in the area of laser technology where it is specifically required to obtain selective spectra which will excite a given laser producing element.

In certain situations, the spectra produced by metallic atoms is required. Therefore, metal, generally in the form=of a fine powder, is introduced into these tubes along with a selected gas to provide the required spectra. Metallic iodides were first used because. these materials, relative to the pure metal, have a high vapor trum required in a given process is obtained. However,

notwithstanding the utilization of high vapor pressure metallic materials, problems have been experienced in maintaining the metal in the atomic or vapor state. Though in a given situation the spectra produced may be usable, it is only a modification of the gas spectrawhile the metallic atom spectra alone is preferred.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a light producing system which overcomes the above noted deficiencies.

' Another object of this invention is to provide a novel flash lamp which yields light of a selected spectra.

Still another object of this invention is to provide a novel process for providing a flash lamp which has better efficiency.

Yet another object of this invention is to provide a novel flash lamp system which contains a high density of metallic atoms in its plasma.

Still again another object of this invention is to provide a novel method for emitting controlled spectra.

Yet, still another object of this invention is to provide a better and more efficient light producing system.

The above object and others are accomplished in accordance with the present invention generally speaking by providing an evacuated tube orenvelope the inner walls of which are coated with a thin film of the desired metal which produces the desired spectra when vaporized by pulsing with current, thus obtaining the desired results. Thus a light producing system is provided whereby specifically selected spectra may be obtained requiring minimum energy for the production of same.

To manufacture the desired structure a metallic wire of the desired material may be suspended in an evacuated tube supported at each end by an electrode. High intensity energy is then pulsed through the wire thereby vaporizing it. The vaporized metallic material will then condense, depositing on the interior of the tube wall. When the tube is to be operated, high intensity energy is pulsed from the electrodes, through the thin metallic film deposited on the interior of the tube wall, thus vaporizing said metallic film (producing a transparent tube wall) which then emits the spectra of the metallic material. In this manufacturing step it is desirable that the level of energy during the ablation phase be sufficiently high so as to ablate the entire wire. Localized ablation of the wire, which might inhibit ablation of the entire wire, can be avoided by utilizing concepts akin to exploding wire techniques. It is known that in utilizing these techniques, that the entire wire may be ablated, whether or not it is of uniform diameter, if a sufficient amount of energy -is' imparted to it. The same technique and similar reasoning is applicable to the metallic film deposition on the inner tube walls. In addition, the metallic film depositions may be said to be self-compensating, i.e. where there is a thin layer there is consequently higher resistivity and, therefore, lower current flow so that the power density is approximately the same in the thin areas as in the thick regions. Therefore, when the layer deposited on the interior of the tube walls, consisting of various degrees of thickness,

is struck by high intensity energy, substantially the enhigh enough, the whole wire will be vaporized rather than locally vaporized. When a wire or film is struck with sufficiently high energy very quickly, the whole tire or film is ablated. In addition, in a film as opposed to a wire, the current energy can, upon reaching a hole or region of thin metallic film,'be avoided by passing around the thin layered section or hole where the resistivity proves to be extremely high.

If, in the method employed above to manufacture the tube, a continuous current carrying path is not established after exploding the wire in the tube, a gas may be injected into the tube and the arc stricken repetitively in the gas until such a continuous current carrying path is established in the metallic film. Then the gas can be pumped out. Furthermore, in the manufacturing step, note that a gas may be injected into the tube before the wire is exploded so as to absorb any effects of the thermal shock necessary to establish the continuous current carrying path on the inner tube walls.

In utilizing the present invention, it is preferable to ablate the metallic film completely every cycle in which the arc is stricken thereby producing an instantaneous high intensity light source. Sufficiently high energy levels are employed which supply the required energy to vaporize the metallic film giving due consideration to keeping this energy at a level so as not to reach the rupture point of the tube walls. This is accomplished by applying a suitable safety factor in the construction of the tube. It is noted that the process of the present invention contemplates striking the metallic film coating the inner surface of the envelope or tube directly with high intensity energy thereby eliminating the necessity of utilizing an intermediate or buffering gas atmosphere. For a given metal and energy input, the spectral output will depend upon the amount of metal used which determines optical properties of the metal and the resistivity of the film. The time dependence of the optical spectra is determined by the vapor pressure of the metal, its heat capacity, its conductivity, its vaporization temperature, the quantity of metal utilized and the time dependence of the applied power. v

The length and diameter of the tube utilized to practice the invention are not particularly critical parameters and may vary over a wide range. The wall thickness, however, ordinarily will be fairly thick so as to add strength to the tube to protect against the shock wave bombardment. Depending upon the particular energy level at which the system is operable, the wall thickness of the tube may vary in a range of from about 1mm to lOmm and preferably, in order to minimize the chance of shattering the tube the thickness will be on the thick side. The material of construction of the tube may be selected from a wide variety of suitable materials. Typical materials utilized for tube construction include quartz, various glasses, Vycor produced by Corning, alkali metal resistant glasses, Lucalux (aluminum oxide Al O polycrystalline material manufactured. by G. E. Yttralux (manufactured by G. E.), and sapphire (aluminum oxide Al O single crystalline form).

The shape of the electrodes utilized in conjunction with the above invention is not particularly critical, however, the size generally should be kept to a minimum and the amount of the protrusion of the electrodes into the tube slight so as to allow' condensation of the metallic atoms behind the electrodes in the tube. The material of construction of the electrodes may be selected from a wide variety of suitable materials. Re-

fractory metals are generally the preferred material in order to obtain optimum results. Typical materials include tungsten, molybdenum, niobium and tantalum. The configuration and spacing of the electrodes is not particularly critical and for the most part depends on the size and shape of the tube.

Any suitable metal may be used in the practice of the process of the present invention. Metals possessing a high vapor pressure and low vaporization tempratures are particularly preferred because of the low amount of energy necessary to vaporize them. Typical such materials include zinc, gallium, indium, thallium, lead, bismuth, tin, mercury, cadmium, metallic alloys and metallic compounds thereof. With due consideration given to the amount of energy required for vaporization, other metals may be used in the practice of the invention. In addition, lithium, sodium, rubidium, cesium, and potassium may be considered for use if the proper envelope materials are taken to protect against corrosion effect when using these corrosive metals. The metals selected would, of course, be dictated by the spectral output required for the particular adaptation of the invention.

The general nature of the invention having been disclosed, the particulars and specifics of the system of the present invention will be more clearly understood by reference to the following drawings of which:

FIG. la 0 illustrate a time sequence followed in producing the lamp system of the present invention.

FIG. 2a c illustrate the cyclic operation of the lamp system of the present invention.

In FIG. la is seen a tube envelope 1 having refractory metallic electrodes 2 sealed into the tube at each end and a metallic wire 3 strung between the refractory metallic electrodes 2. In FIG. 1a, a current generating means 4 is applied across these electrodes after the tube has been evacuated thereby instantaneously vaporizing and/or ablating the strung wire. In FIG. 1c, the current generating system is disconnected and the vaporized metal is allowed to coat the tube walls and form an electrically continuous path between the two electrodes. As previously mentioned, if a continuous electrical path does not develop upon initially ablating the strung wire, an arc may be struck again until such a condition is produced with the addition of gas, if desired, to cushion the shock waves produced if employed, the gas is then removed by conventional evacuation techniques through one of the electrodes having a passage for the gas as shown. I

In FIG. 2a is seen the tube envelope 1 as previously described with the continuous current carrying path metallic film 5 developed between the electrodes 2. In FIG. 2b, a current pulse is provided across the electrodes from a conventional current generating system not shown causing current to flow through the metallic film connecting the electrodes resulting in the instantaneous vaporization and/or ablation of the metallic film 5. The hot metallic gas is seen to fill the tube volume and emit light. In FIG. 2c, the current generating system is disconnected from the tube allowing the metallic gas to cool and recondense on the tube walls forming a continuous electrical path between the electrodes 2 so that the lamp is now ready to be recycled and reignited.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To further define the specifics of the present invention the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated. The energy (voltage) in the capacitor may be varied so as to yield various modifications of the metallic spectra (lines, continuum or intermediate modifications thereof).

EXAMPLE I A tube of Lucalux material manufactured by G. E. Company, about 15 cm in length, about 0.5 cm internal diameter and about 1.5 cm outside diameter, containing two electrodes is provided. The pointed electrodes, a 291 1.--..2.m n ameter a e cqnsttuqtedpt n obium metal and protrude into the tube about 0.3 cm. Sodium metal is distilled into the tube in a quantity of about 23 mg. The lampis evacuated, sealed and placed in an isothermal oven at about 700C and then very slowly cooled until a continuous current carrying path is es-.

tablished within the tube. The resistance of the uniform QQil .@IP. isab utA 2919:? shmslhe lim srgfa asi capacitor is energized and discharged into the tube thus vaporizing the metallic deposition on the inner tube walls resulting in the desired spectra.

EXAMPLE ll A tube is constructed of quartz material having a length of about cm and a diameter of about 0.4 cm internal diameter and about 1.5 cm outside diameter enclosing two electrodes spaced about 9.6 cm apart. The pointed electrodes are constructed of tungsten material and protrude into the inner tube about 0.2 cm. A

wire of thallium metal 0.45 mm in diameter is suspended between the electrodes. The tube is then evacuated. A 10 microfarad capacitor is charged up and then discharged to the electrode thereby abfitin g the wire and resulting in a condensation of metallic atoms all over the inside of the tube walls. The capacitor is then energized and discharged into the tube thereby vaporizing the metallic deposition of the inner walls resulting in the desired spectra.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used if desirable. For example, a combination of metals or of metals and their compounds may be used to provide any one of a number of desiredspectra. A wide va riety of specially treated glasses and plastics maybe used in constructing the tube envelope. Other methods may be used in constructing the tube and practicing the invention comprising a solid solution of two or more metals or their compounds ablated within the tube to provide the desired metallic deposition on the inner tube walls. In addition, other materials may be incorporated in the tube walls or electrodes which will enhance, synergize or otherwise desirably affect the properties of the systems for their present use. For example, a buffering gas which desirably modifies the metallic spectra may be introduced to absorb the shock produced by vaporization of the metallic material.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of the invention.

What is claimed is:

l. A reusable flash lamp comprising an evacuated substantially transparent envelope, a substantially pure metal deposit on the interior walls of said envelope, electrodes operatively disposed within said envelope, and an electrical power source capable of energizing said electrodes, said electrodes being adapted to sustain an arc discharge therebetween of sufficient magnitude from energy supplied by said power source to vaporize the metal deposit independent of additional external means.

2. The lamps as described in claim 1 wherein said metal is selected from at least one member of the group consisting of indium, gallium, thallium, mercury, sodium, potassium, strontium, ytterbium, radium, barium, europium, calcium, magnesium, lithium, rubidium, cesium, zinc, lead, bismuth, tin and cadmium.

3. The lamp as described in claim 1 wherein the metallic composition is a pure metal.

4. The lamp of claim l, wherein the metal is one possessing a high vapor pressure.

5. The lamp of claim 1, wherein said metal is readily vaporizable.

UNITED STATES PATENT OFFICE" CERTIFICATE OF CORRECTION Patent No. I 3781585 I I D d December 25. 1973 Inventor(s) Charles F. Gallo rs in the above-identified patent 1 It is certified that error appea by corrected as shown below:

and that said Letters Patent are here 1'. Celumn '1, line l4--'Ihe word "enrgy" shoflld be--energy--.

2 Columnl, line l9 -'Ihe .word "spctra" should be--spectra.

line 45--'Ihe word "tire'f should be -wire-"-.

3. Column 2,:

Signed and. sealed this 3rd day of December 1974.

(SEAL) Attes't:

MCCOY M. GIBSON JR. c. MARSHALL DANN Arresting Officer Commissioner of Patents USCOMM-DC 60,376-P69 FORM Po-ms'o (10-69) I GOVERNMENT PRINTING OFFICE I969 O-JIS-JSI, 

2. The lamps as described in claim 1 wherein said metal is selected from at least one member of the group consisting of indium, gallium, thallium, mercury, sodium, potassium, strontium, ytterbium, radium, barium, europium, calcium, magnesium, lithium, rubidium, cesium, zinc, lead, bismuth, tin and cadmium.
 3. The lamp as described in claim 1 wherein the metallic composition is a pure metal.
 4. The lamp of claim 1, wherein the metal is one possessing a high vapor pressure.
 5. The lamp of claim 1, wherein said metal is readily vaporizable. 